The present invention relates to a device for controlling fires and, more specifically, to a device for preventing lubricating oil fires resulting from the fracture or separation of an oil line at the bearing of a machine having a pressurized lubricating system.
The hazard of lubricating and hydraulic oil fires in electric generating stations has been of concern for many years. In 1964 the National Fire Protection Association published a pamphlet on fires in electric generating plants and highlighted three fires involving the spray of oil from broken oil lines. The total loss, in 1988 dollars, was $15,000,000. The inventor is aware of twenty-four fires of this type between 1951 and 1988, with a total estimated loss of $125,000,000. Many of the fires burned until the lubricating oil was able to be shut off or its supply was exhausted. By the time the cause of the fire was determined and the spraying of oil from the failed oil line was able to be stopped, damage of many millions of dollars had already occurred.
In pressurized lubrication systems, such as those used for steam and gas turbines, internal combustion engines, and rotating and reciprocating compressors, lubricating oil is delivered to the bearings at pressures of up to 35 psig. The flow to each bearing is controlled by a metering orifice in the bearing housing. This orifice reduces the pressure of the lubricating oil to atmospheric pressure in the bearing area.
Lubricating oil fires often occur around the systems described above as a result of the fracture of an oil pipe to a bearing or the separation of such an oil pipe from its connections. The oil under pressure sprays out at the point of failure in a fine mist, which is readily ignited by adjacent hot surfaces or by other mechanisms. The resulting fire is torch-like, with a very high rate of heat release, such that the fire may ignite or overheat building structure and contents up to sixty feet away from the point of spray origin.
Water sprinkler discharge, or even water spray discharge directly on the oil pipe at the point of oil release, is known to be ineffective in extinguishing or controlling such fires. Water may limit the damage caused, by cooling the target material or structure, if the water can be directed properly. The only effective extinguishments have been total-flooding agents, such as the Halons, and carbon dioxide. However, the use of these agents requires that the machinery protected from the fire be enclosed in a housing which can be sealed off to retain the necessary concentration of the extinguishing agent for as long as there is a danger of reignition. This is not usually practical, other than for some gas turbine installations.
Oil-spray fires of the type described above are very similar to leaking gas fires in that the principal approach to the extinguishment of both such fires is to shut off the flow of the flammable fluid. However, in most installations affected by oil-spray fires, auxiliary oil pumps continue to pump oil to the bearings of the machinery after the machine is tripped off line. The problem here is that the oil lines in which the failures occur supply the bearings of huge and very expensive steam turbines rotating at very high speeds. The lubricating oil cannot simply be cut off to stop the fire, since very extensive damage is likely to occur as a result of the failure of the bearings and the damage that the failure of the bearings would have on the spinning turbines. Therefore, the flow of oil is maintained to protect the bearings while the machine is coming to a stop and, in the case of large steam and gas turbines, after it has been put on turning gear for slow rotation during cooldown.